Sometimes it's not a good reason,
Isn't the point of your database to help people find quality stories? If the reason why lots of people review it is "sometimes not a good reason," then the story's not really quality.
You will note that I mentioned the flaw that a story must usually gain reviews to be noticed, and for that you just have to keep checking the listed of updated stories, use recommendations by authors you like, and check communities of the particular flavours of story you prefer.
People who visit FFNet do this anyway
without tools. That's how lots of authors end up with groupies -- because it's the norm over there to follow one author and check out his or her recs. Not to mention that's why FFNet provided us with a way to filter stories by genre, character, word count, et cetera.
Additionally, while I understand that you're trying to make it easier on yourself, you're not really helping people to actually find quality. As Giratina said, there's a lot of awesome writers in that category who never get exposure because their stories just don't center around things that are in vogue at the time. This doesn't mean they're bad or that someone who gets more reviews most likely has a better story. They just don't have subjects that appeal to the average reader on there -- and, unfortunately, the average reader tends to have sheep-like tendencies that force them to completely ignore otherwise decent stories in favor of something that's not exactly quality but is still about something that appeals to them.
Hilariously (for me), I actually have an example of this on my own profile. Currently, the story I've spent almost two years writing, Anima Ex Machina, is on FFNet. So is Momentum, a story I spent two weeks (so far) writing. AEM has seven chapters on there, all of decent quality if I may say so myself (although I need to edit them), and as you can probably tell by the reviews here, the story's not a generic new trainer plot. Momentum is currently a PWP fic with only two chapters to it and probably the driest attempt at a narrative I've written since high school. AEM has nine reviews. Momentum: twenty-four, not counting the numerous PMs I've received concerning it. The difference? AEM is not about something that's currently in style. Momentum is a submit-your-own OC story, and that happens to be in fashion now. Is Momentum a better story than AEM? Pfft, no. Hell, I don't even know what the story
is as of current, and I almost want to torch the first chapter.
Point is, I'm more inclined to view the
underdogs (the ones that
don't get reviews that often) as being better fics overall compared to the big-name fics on FFNet. This is because there's a lot of gems that are just new, fresh, and not afraid to play with never-been-touched ideas, but that sort of thing only appeals to a small percentage of the audience. Of course, this is naturally just my opinion, and the aforementioned sheep might disagree with me (and potentially claw my eyes out over calling them sheep).
Likewise, one should take into consideration the fact that there's a lot of people out there who aren't sociable authors and therefore are great writers who rarely get reviews. Meanwhile, you might have a sociable author who's writing a generic shippy story but just has a lot of groupies who're backing their story because the author backed theirs.
Tl;dr, there's a lot of factors that go into finding quality fics on FFNet, and it's unfortunately an exercise of sifting through for the diamond in the rough. There's no real easy way to do it without being horrendously biased. Of course, if sorting by review count works for you, then by all means, do it, but it's not going to work for everyone (like yours truly), sorry to say.
Tl;dr to the tl;dr: Fanfiction.net = exercise in
Your Mileage May Vary. (Insert standard TVTropes warning here.)